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Kernel: Shrink instead of expand sigaltstack range to page boundaries

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Since the POSIX sigaltstack manpage suggests allocating the stack
region using malloc(), and many heap implementations (including ours)
store heap chunk metadata in memory just before the vended pointer,
we would end up zeroing the metadata, leading to various crashes.
This commit is contained in:
Idan Horowitz 2023-12-24 15:53:16 +02:00 • committed by Andreas Kling
parent 4c6fd454d0
commit a49b7e92eb
5 changed files with 29 additions and 34 deletions
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2
Kernel/Tasks/Process.h
View file

@ -688,7 +688,7 @@ private:
ErrorOr<GlobalFutexKey> get_futex_key(FlatPtr user_address, bool shared);
ErrorOr<void> remap_range_as_stack(FlatPtr address, size_t size);
ErrorOr<Memory::VirtualRange> remap_range_as_stack(FlatPtr address, size_t size);
ErrorOr<FlatPtr> open_impl(Userspace<Syscall::SC_open_params const*>);
ErrorOr<FlatPtr> close_impl(int fd);

18
Kernel/Tasks/Thread.cpp
View file

@ -752,8 +752,7 @@ void Thread::reset_signals_for_exec()
m_have_any_unmasked_pending_signals.store(false, AK::memory_order_release);
m_signal_action_masks.fill({});
// A successful call to execve(2) removes any existing alternate signal stack
m_alternative_signal_stack = 0;
m_alternative_signal_stack_size = 0;
m_alternative_signal_stack.clear();
}
// Certain exceptions, such as SIGSEGV and SIGILL, put a
@ -881,15 +880,12 @@ bool Thread::is_signal_masked(u8 signal) const
return (1 << (signal - 1)) & m_signal_mask;
}
bool Thread::has_alternative_signal_stack() const
{
return m_alternative_signal_stack_size != 0;
}
bool Thread::is_in_alternative_signal_stack() const
{
auto sp = get_register_dump_from_stack().userspace_sp();
return sp >= m_alternative_signal_stack && sp < m_alternative_signal_stack + m_alternative_signal_stack_size;
if (!m_alternative_signal_stack.has_value())
return false;
return m_alternative_signal_stack->contains(VirtualAddress(sp));
}
static ErrorOr<void> push_value_on_user_stack(FlatPtr& stack, FlatPtr data)
@ -1025,12 +1021,12 @@ DispatchSignalResult Thread::dispatch_signal(u8 signal)
m_signal_mask |= new_signal_mask;
m_have_any_unmasked_pending_signals.store((m_pending_signals & ~m_signal_mask) != 0, AK::memory_order_release);
bool use_alternative_stack = ((action.flags & SA_ONSTACK) != 0) && has_alternative_signal_stack() && !is_in_alternative_signal_stack();
bool use_alternative_stack = ((action.flags & SA_ONSTACK) != 0) && m_alternative_signal_stack.has_value() && !is_in_alternative_signal_stack();
auto setup_stack = [&](RegisterState& state) -> ErrorOr<void> {
FlatPtr stack;
if (use_alternative_stack)
stack = m_alternative_signal_stack + m_alternative_signal_stack_size;
stack = m_alternative_signal_stack->end().get();
else
stack = state.userspace_sp();
@ -1042,7 +1038,7 @@ DispatchSignalResult Thread::dispatch_signal(u8 signal)
.uc_stack = {
.ss_sp = bit_cast<void*>(stack),
.ss_flags = action.flags & SA_ONSTACK,
.ss_size = use_alternative_stack ? m_alternative_signal_stack_size : 0,
.ss_size = use_alternative_stack ? m_alternative_signal_stack->size() : 0,
},
.uc_mcontext = {},
};

4
Kernel/Tasks/Thread.h
View file

@ -884,7 +884,6 @@ public:
u32 pending_signals() const;
u32 pending_signals_for_state() const;
[[nodiscard]] bool has_alternative_signal_stack() const;
[[nodiscard]] bool is_in_alternative_signal_stack() const;
FPUState& fpu_state() { return m_fpu_state; }
@ -1177,8 +1176,7 @@ private:
u32 m_pending_signals { 0 };
u8 m_currently_handled_signal { 0 };
u32 m_signal_mask { 0 };
FlatPtr m_alternative_signal_stack { 0 };
FlatPtr m_alternative_signal_stack_size { 0 };
Optional<Memory::VirtualRange> m_alternative_signal_stack;
SignalBlockerSet m_signal_blocker_set;
FlatPtr m_kernel_stack_base { 0 };
FlatPtr m_kernel_stack_top { 0 };